1. Field of the Invention
The present invention relates to a rewritable magneto-optical memory device for multi-wavelength recording and reproduction.
2. Description of the Background Art
Conventionally, a medium such as TbFeCo is widely known as a magneto-optical recording medium, in which the writing is made in a heat mode using the light as a heat source, and the reading is made by utilizing the Kerr effect.
However, a thin film formed by such a conventionally known magneto-optical recording medium has a large optical absorption loss, and in addition, there has been no known method to realize the multi-wavelength recording by using such a conventionally known magneto-optical recording medium, so that the magneto-optical multi-wavelength recording and reproduction has not been realized conventionally.
Moreover, it has been conventionally known that the packing density can be improved by piling up multiple layers of the magnetic films, but in a case of writing the recording bit selectively on a desired layer of the multi-layered magnetic films, it is indispensable to realize the focusing to the desired layer by using a lens so as to increase the temperature of the multi-layered magnetic films locally, without affecting the other layers of the multi-layered magnetic films. However, conventionally, a technique for focusing each of the very thin film layers selectively has not been realized in practice.
Furthermore, even if it becomes possible to write the recording bit somehow, the reproduction of the recorded signal components from the desired layer of the multi-layered magnetic films has been very difficult because the light signals from all of the multi-layered magnetic films are superposed each other at a time of the reproduction.